Siljanovska Petreska Gordana, Salsamendi Maitane, Arzac Alejandro, Leal Gracia Patricia, Alegret Núria, Blazevska Gilev Jadranka, Tomovska Radmila
POLYMAT and Departamento de Química Aplicada, Facultad de Ciencias Químicas, University of the Basque Country UPV/EHU, Joxe Mari Korta Center, Avda. Tolosa 72, 20018 Donostia-San Sebastian, Spain.
CIC biomaGUNE, Carbon Nanobiotechnology Group, Miramon Pasealekua 182, 20009 Donostia-San Sebastián, Gipuzkoa, Spain.
ACS Omega. 2017 Aug 2;2(8):4123-4131. doi: 10.1021/acsomega.7b00184. eCollection 2017 Aug 31.
When graphene is used as SERS substrates, it contributes to the chemical mechanism (CM) of enhancement of Raman signal, owing to which the detection limit is very low (lower than mM content of probe molecules). The CM of enhancement depends largely on the interactions between the substrate and the probe molecules. Therefore, in this work, we have investigated the possibility of increasing the SERS activity of graphene by improving the interaction between the probe molecule and the graphene substrate by establishing exclusively strong covalent bonding between them. Fluorescein (Fl) was selected as a probe molecule because it is one of the most commonly used fluorophore in bioscience. As a graphene substrate, reduced graphene oxide (rGO) platelets were used. In addition, silver nanoparticles (AgNPs) were added onto the hybrids to further increase the enhancement by electromagnetic mechanism. Highly enhanced Raman signal of Fl onto neat rGO was achieved for micromolar concentration of the probe molecules. This was attributed to the covalent bonding between them, which introduced hole doping to rGO, decreasing the Fermi level of rGO and bringing it more closely to the LUMO of Fl. This induces aligning of their energy levels, resulting in higher contribution of the nonresonance effect to the charge transfer mechanism of enhancement, which, in this case, occurred intramolecularly. When AgNPs were added onto the rGO substrate, the expected enhancement performance was not observed. On the one hand, this was attributed to small size (∼20 nm) of AgNPs and lack of aggregates and, on the other, due to the unusually high contribution of CM determined.
当石墨烯用作表面增强拉曼散射（SERS）基底时，它有助于拉曼信号增强的化学机制（CM），因此检测限非常低（低于探针分子的毫摩尔含量）。增强的化学机制在很大程度上取决于基底与探针分子之间的相互作用。因此，在本工作中，我们研究了通过在探针分子与石墨烯基底之间建立排他性的强共价键来改善它们之间的相互作用，从而提高石墨烯的SERS活性的可能性。选择荧光素（Fl）作为探针分子，因为它是生物科学中最常用的荧光团之一。使用还原氧化石墨烯（rGO）片层作为石墨烯基底。此外，将银纳米颗粒（AgNPs）添加到杂化物上，以通过电磁机制进一步增强信号。对于微摩尔浓度的探针分子，在纯rGO上实现了Fl的高度增强拉曼信号。这归因于它们之间的共价键，该共价键给rGO引入了空穴掺杂，降低了rGO的费米能级并使其更接近Fl的最低未占分子轨道（LUMO）。这导致它们的能级对齐，使得非共振效应在增强的电荷转移机制中贡献更大，在这种情况下，电荷转移发生在分子内。当将AgNPs添加到rGO基底上时，未观察到预期的增强性能。一方面，这归因于AgNPs的尺寸小（约20 nm）且缺乏聚集体，另一方面，归因于所确定的化学机制的异常高的贡献。
